Simple EQ for Neve 1290

[Spencerleehorton]

I’m assuming the inverting amps input is C and output is E and all it’s doing is inverting the control?

Why is all my signal so low when I engage the eq?

And the peaks for when I adjust are really subtle I know I’m only putting in a sign wave and this will make a difference when I put it more frequencies

 

[wlinart]

To figure out how everything is connected, i found this schematic really helpfull: https://www.soundskulptor.com/docs/eq573-schematic-01.pdf, on page 2 it shows perfectly how the connections are made with each amp. Maybe it helps you too. I gave it a quick look, and it looked like you were missing a connection between C and E or C and M on the inverting amp. But please check that first yourself, because i'm not 100% sure.

If the level drops, i would first try to change the order of the amps, check if the problem follows the amp or not. What i mean is, there are 2 identical inverting amps on the ba284 for the eq, try connecting the first amp where you now connected the second and vice versa. If the problem is still with the same band, you know it's not the amp. otherwise, the problem is with the amp.

 

[Spencerleehorton]

Yeah good idea about changing the amps, so far I believe K and M to be working correctly as when I just ha e b211 and b182 connected its very nearly working great, the only thing I would say is that the eq looks a little louder when on than in bypass.
The drawing I did before I made a mistake so I’ve corrected and it’s below.

Inverting amp C to E seems to be my problem as I’ve tried another b205 Pcb in and it is exactly the same?

Will try using just K and M inverting amp And see if I get good signal.

 

[Spencerleehorton]

Just the same problem with the other amp, so i will try the other channel incase both inv amps are not working, if they dont work I aint got a clue whats going on??
I can see its all working, just the level is way down, must be something earthing out somewhere maybe?
Im using polyester caps, rather than polystyrene? but dont think that would be a problem with level? maybe i have a dud cap?

 

[ruffrecords]

Thanks Ian that was really helpful apart from you put "The mic pre output is from pin P of the BA284" which i think you meant P from BA283, as P on BA284 i think is for higher gain settings?

Yes I meant pin P on BA 283, sorry.

on B205 where should M go? I've got it back into H at the moment?

No, you can see on the schematic that M on B205 goes to pin C on BA284. H goes to pin E on BA284. Just follow the schematic posted by krabbencutter.

Cheers

Ian

 

[Spencerleehorton]

Yeah I get all the connections now and believe I have it correct it’s just the inverter amps I think are not working.
I need to just look at them and make sure they are tip top.
Is there a basic way of testing that they are correct?

 

[alexc]

Signal tracing with R E W 

 

[Spencerleehorton]

I have a scope but interested in what you said about REW, you have a link to your info?

There is no point in tracing signal in these inverter amps if they don’t work and They lower the signal when I put them in circuit, will check voltages on transistors and see if off.

 

[alexc]

I do subscribe to the view that one 'traces signal'  as they go and just as soon as things power up and don't release smoke  ..  over the first 30s to a couple of minutes or so.

I don't say that with sarc - it's very much the challenge most of the time.

So - of course, if you have modules or sub-assemblies that are suspect then all bets are off.

Apart from that, I find less effort overall if I get the signal 'true' as best as possible    'as I go'.

Most audio schmutz is 'cumulative' so the sooner you get onto it, the better!

..

R E W from  mr John Mulcahy and Co    is  the best thing since 'sliced cheese'      ...  fine audio analysis on the 'cheap' 

[100usd interface +  Room Eq Wizard concept ]

Works great 'standalone'    ie  it is a fine signal generator  *and*  spectral analyser    in near continuous 'real time'

For nix!

...

The beta versions which are the Biz  do require a registration at 'AV Nirvana'  site ...  it's essentially  'donation ware' and easily worth a small pile of gold 

I just can't imagine    'not using it'    to do any serious audio analysis - like some of these adventures in DIY 

..    in conjunction with my multi-meters,  4-chn Tektronix  *and*  DIY    'Audio Probe-ulator' 

Really

 

[Spencerleehorton]

I was thinking a about getting a hantek 6022 at some point as my scope is pretty old and decrepit, I have REW what interface would you use with it ?

 

[ruffrecords]

Yeah I get all the connections now and believe I have it correct it’s just the inverter amps I think are not working.
I need to just look at them and make sure they are tip top.
Is there a basic way of testing that they are correct?

First thing to do is go round and check all the dc voltages are correct. There are three on the PCB so it is easy to compare them. Unless you have the same broken component or made the same assembly error on all three there's a good chance of finding the fault just by comparing them. Check especially the emitter of the third transistor which should be close half the supply voltage.

Cheers

Ian

 

[Spencerleehorton]

Perfect ian, I’m on holiday for a week, back on it from 17th, hopefully get to the bottom of why I’m having so many problems!!!

 

[alexc]

For tracing 'signal' in DIY builds  ..  especially if one is  'directly probing'  [ie the DIY 'prob-ulator' concept], I do recommend something fairly cheap. 

If one is brave enough to venture to probing higher voltages, meaning larger ac audio signals and possibly [often!] in the presence of dc voltages  a 'cheap-ish' audio interface is best.

One wouldn't be 'ping-ing' their expensive  interface with some hokey  'probe'  planted in some 'unknown diy', for example.

lol the 'Lady and the Tramp' scenario  ;D

For cheap,  I like [personally] M-Audio stuff on the PC - they do do Mac as far as I know.

I use a 'four analog i-o plus two digital'  in this role  ...    one channel of i-o for 'loopback reference', one channel for 'device under test' (send and return to your DIY)  .. all balanced preferably.

The other stereo analog i-o is good for 'monitoring'  [ie. for playing media while you go, completely seperate from the testing]

And a stereo digital pair of i-o  is good for independant 'digital perspectives'.

I use M-Audio Pro 610 Firewire  ..  I think with change from said hundred dols us. But it could be anything you like.

Basically cheap, with something like at worst, 0.015% THD+N at near full-scale output  and with a 'hum floor' of around 120 dB [below said near full-scale output]. Most do way better, of course ..  but this is the 'cheap' seats.

I find they do around 10Vpp or so input and/or output  ..  at near full-scale levels with said level of distortions, before really borking out.

..

So that would be i) cheap  ii) balanced  iii) sufficient I-O

...

For stuff like discrete circuits at +24V supply, I think it does pay to make your own DIY 'prob-ulator' 

It is basically  a probe with a dc blocking cap [to block dc!] and a parallel resistance of some moderately high Mohm value [to not load down your 'signal under test'].

Better ones go into an 'attenuator box' to conveniently    'match'  or 'map'      your 'ac signal under test'      to your interface 'available signal range Vpp'.

Again, it's more complicated to describe than to do. Once you get going, it's a breeze and you can probe at will without fear of the  'troubles'.

....

In R E W that means HD  quality signal  send, and return which can be 'visualised' in 'near real time' and mostly without 'glitches' 

ie.  spectral analysis, sweep analysis and quite groovy 'CRO' type voltage waveform measurement.

This relatively 'new' feature of  R E W  is far, far more accurate and with much greater resolution than my  trusty Tektronix 4chn CRO  [analog cro with digital control and fab measurement cursors].

I don't even want to mention the flexible 'triggering',  nicely  done 'deep trace buffer'  [for the voltage waveform capture]  or the attendant 'after the fact' [historical ]  voltage waveform  visualisation capabilities.  8) - they are  something else  ..  along with available 'trace math' functions on the dual channels casually  at one's disposal.

The accuracy is superb ... it eats up signal levels of even few fractions of micro-Volts peak-to-peak.

....

Reliability, in terms of the mundane things like 'crashes' is legendary and is a proper and fitting testimony to the rock solid stability  ...  no crashee or bsods here thanks muchly! 

As I alluded to previously [befoor] - I like to play media [at the same time, on  the same computer] whilst I'm doing all this  ..  for many long hours at a stretch ..  usually Art Bell's Coast-to-Coast radio broadcasts from wayback, with really interesting peoples, like mr Graham Hancock  and similar. 

[circa 2016 amd 8-core box , win7_64, lotsa mem and SSDs and about 140VA of  power used with a 23" Samsung monitor]

No probs whatever. Same with browsing the net,  or even most network file operations going on too.

And finally,  install/un-install/upgrades  processes  are  almost 'a pleasure - ' it's so quick and 'lightweight' - haven't yet had to 'step back' even once on any revision in all the years of  REW. 

Even so to the point where REW is a fine 'benchmark' app for audio subsystems - I use it to 'stress test' wannabe audio PCs

...

That's basically it.  Carry on

 

[krabbencutter]

Don't want to derail too much from the topic, but for cheap usb audio interfaces the UMC HD interfaces from Behringer are hard to beat. And if you're thinking about a usb oscilloscope, I can recommend pico technologies. Their software support is top notch! I invested in a 2204A last year and its a joy to use.

As for the inverting amps, you could try just using something like an LM358 for the BA284. Connect your circuit to the inverting-input & output and the non-inverting input to ground.

Also shout out to team Germany, this forum needs more Weltschmerz! 

 

[alexc]

And more of the other great things about REW Audio Analysis and Visualisation software  are :

1. asio drivers for all your high performance including the very high sample rates ie. 24bit 96KHz and beyonders

2. fantastic 'historical' visualisations  for  'after the test' compares  even across different test events  [all nicely stored with REW files in a bespoke 'browser'  ...  which can load multiple REW data files  ..  for the further mess-ing with  / aggregation activities ]

3. snapshot facilities built in  *but*  even better is ease of use of the 'host' platform  facilities for 'snapshot' annotation and the like

      -> this is great because in the 'rough and tumble' world of DIY audio, one needs to be able to 'substantiate perf claims'
      -> for the real loonies, you can do host 'screen video capture'  to really lay it on thick at YouTube

Once you get a 'system' going, you can easily generate many annotated 'snaps' or video 'snips' for 'tracability'.
  ->  In the world of engineering for  'quality assurance' type ops, this is the money feature. 

...

Things that R E W does that  goes    'way beyond' are  :

-  everything REW with respect to it's  'heads up THD displays' in real time.
      ->  this is peerless in my experience

-  a variety of measurement units ...  everything from dBFS, dBu, nV/sqrt(Hz)           
                                to plain ol'  Volts  - take your pic!  [sorry yet another pun]
      -> enough to keep even your best boffin baffled

- measurement cursors  at every which-way  including smart-mouse-enabled zooming, slicing and dicing of measurement axis
      -> this is again peerless

and  plenty more!

...

Here's an example of a 'half-minute' in my diy life  ..

 

[Spencerleehorton]

Are you saying use a LM358 or similar general purpose opamp instead of the inverting amps on the 284?

 

[krabbencutter]

Are you saying use a LM358 or similar general purpose opamp instead of the inverting amps on the 284?

Reading it that way feels like blasphemy but yes, that's exactly what I'm saying  ;D

 

[Spencerleehorton]

Ah ok so 24v to pin 8 and gnd pin 4 then pin 2 and 3 input and out for inv amp 1 then 6 and 7 for inv amp 2, I’m sure I can cram that in there to test then if it works I’ll replace the inv amps on the Pcb 284.
I have loads of other opamps to try but will have to check their voltages and functions.

 

[Spencerleehorton]

I’ve invested in a hantek 6022be now so should be able to do all these new tests etc and get my preamps and outboard sounding much better!!!

 

[Spencerleehorton]

As regarding the inductors I would like to discuss the fact that my inductors DCR is much lower than the winding sheets I have got from CJ,
My DCR for instance on the 10H is 151R and on the original wound ones it should be 700R.
As my one was wound on 6000AL with 1300 winds and the original was on 800 AL with 3500.

Would one have a better peak etc?

If I was to add resistance would it help or is mine better?